The present invention relates to a lighting apparatus and a liquid crystal display, more specifically to a lighting apparatus which can light with a uniform light intensity, and a liquid crystal display using the lighting apparatus.
Liquid crystal panels, which are thin and light, are widely used as display screens of portable information terminals.
The liquid crystal panels contain transmission type liquid crystal panels and reflection type liquid crystal panels.
FIG. 28A is a sectional view of the transmission type liquid crystal panel. As shown in FIG. 28A, a deflector 214 is sandwiched between a glass substrate 210 and a glass substrate 212. Bus lines 216, etc. are formed on the glass substrate 212. Liquid crystal 220 is sealed between the glass substrate 212 and the glass substrate 218. A color filters 224a, 224b, 224c are sandwiched between the glass substrate 218 and the glass substrate 222. A deflector 228 is sandwiched between the glass substrate 222 and the glass substrate 226.
FIG. 28B is a sectional view of the reflection type liquid crystal panel. As shown in FIG. 28B, the reflection type liquid panel has a mirror 230 sandwiched between a glass substrate 210 and a glass substrate 212. The mirror 230 reflects light introduced from above the upper surface of the reflection type liquid crystal panel.
Liquid crystal itself, which does not emit light, needs lighting to visually recognize information on the liquid crystal panels.
In the transmission type crystal liquid panel, the lighting apparatus is disposed below the liquid crystal panel.
In the reflection type liquid crystal panel, in visually recognizing the display screen in circumstances where light, such as sunlight, room lights, are present, the lighting apparatus is not essential. However, the lighting apparatus is necessary to enable the visual recognition also in circumstances where no light is present. In the reflection type liquid crystal panel, the lighting apparatus is disposed above the liquid crystal panel.
FIG. 29 is a perspective view of a proposed lighting apparatus. As shown in FIG. 29, the proposed lighting apparatus includes LEDs 112a, 112b which emit light, a linear photoconductor 114 which transforms light from the LEDs 112a, 112b to linear light and emits the linear light, and a plane photoconductor 116 which transforms the linear light from the linear photoconductor 114 to plane light and emits the plane light. A plurality of light reflection portions 120 are formed in stripes on the back side, i.e., the reflection side of the linear photoconductor 114. A reflection coat film 118 is formed on the reflection side of the linear photoconductor 114.
FIGS. 30A and 30B are a perspective view and a plan view, respectively, of the linear photoconductor of the proposed lighting apparatus. As shown in FIGS. 30A and 30B, light emitted by the LEDs 112a, 112b is reflected on the light reflection portions 120 formed on the back side, i.e., the reflection side of the linear photoconductor 114. The light linearly emitted from the emission side of the linear photoconductor 114 is transformed to plane light by the plane photoconductor 116 and emitted from the plane of the plane photoconductor 116.
Such proposed lighting apparatus can light the liquid crystal panel in plane.
Such proposed lighting apparatus is described in the specification of Japanese Patent Laid-Open Publication No. Hei 10-260405/1998.
However, the above-described proposed lighting apparatus cannot light the liquid crystal panel 108 with a uniform intensity as will be described below.
FIG. 31 is a diagrammatic view showing relationships between the human eye and the display screen. When the display screen of the liquid crystal panel 108 having a 2 inch (5.08 cm)-screen size is visible at a 350 mm-distant position, light forming 0 degrees to the center of the display screen arrives at the eye, and light forming ±3 degrees to both ends of the display screen reaches the eye.
As shown in FIG. 32, in the proposed lighting apparatus, the intensity distribution of light emitted from the linear photoconductor 114 is not uniform and has high light intensities and low light intensities. An intensity distribution of the light emitted from the linear photoconductor 114 is reflected on an intensity distribution of the light emitted from the plane photoconductor 116. The intensity distribution of the light emitted from the plane photoconductor 116 is not accordingly uniform and has high light intensities and low light intensities. Accordingly, a liquid crystal display using the proposed lighting apparatus cannot have good display characteristics.
As shown in FIG. 32, in the proposed lighting apparatus, the intensity distribution of light emitted from the linear photoconductor 114 is not uniform and has high light intensities and low light intensities. An intensity distribution of the light emitted from the linear photoconductor 114 is reflected on an intensity distribution of the light emitted from the plane photoconductor 116. The intensity distribution of the light emitted from the plane photoconductor 116 does not accordingly uniform and has high light intensities and low light intensities. Accordingly, a liquid crystal display using the proposed lighting apparatus cannot have good display characteristics.